The 3 contenders are currently finalising their final responses to the CEP with 5 days to go. But it is US and Australian alliance dynamics and the electrical power needs of the US provided AN/BYG-1 combat system that may be thoroughly under-rated issues. Combat systems are the networks of sensors, weapons, data bases and other electronics that submarines rely on and fight with."
In terms of alliance dynamics Submarine Matters' The US Continues to Influence Australia's Future Submarine Selection in Many Ways, September 22, 2015, pointed out that US alliance issues include:
1. Australia's on the record preference for the US AN/BYG-1 combat system,
2. Given the highly confidential nature of combat system it may be effectively up to the US which of the 3 countries can access the combat system technology, and
3. The US public endorsement of the Japanese Soryu submarine as the best large submarine may be a continuing US policy. "Vice Adm. Robert Thomas, commander of the U.S. Navy’s 7th Fleet, said Oct. 24  in Tokyo that then-Australian Defence Minister David Johnston was very interested in Japan’s Soryu-class subs. “I talked to him about it four years ago and I said: ‘You want to find the finest diesel-electric submarine made on the planet - it’s made at Kobe works in Japan,’"
Now a sheer physical requirement may also be crucial. That requirement is high electical power needs of the US combat system and for the high transit speeds required of Australian submarines. Its needs are probably more like the needs of Japan's part US derived combat system and less like Germany's and France's air independent propulsions (AIP) compatible lower power combat systems. AIP only delivers a small amount of power while the US combat system is built around the power output of its largest user group - which are large, high electrical power producing, US nuclear submarines.
Anonymous [on Nov 21, 6:37PM] commented: "...A. It is not the Max speed that matters, it is the transition [transit] speed that is critical for Australia. The batteries of the submarine are consumed by 2 factors: the propulsion load and hotel load (stuff like air conditions, lights, combat systems...etc). The propulsion load is about the square or cubic of the speed. So, if you want to double the speed, you need about 4 times (2X2) or 8 times (2X2X2) of propulsion load.
And so, how does the Type 212/214 achieve that "superior" endurance? Sail at very slow speed (4 to 5 knots), very low crew numbers and a much less power hungry but less capable combat systems (so much less hotel load). It takes 2 weeks to cover 1500km, and [Australian] submarines have to sail nearly 7,000km to reach the operation area. If we do it in German's way, we have to return to base (with 70 days provision as in Collins) before we reach our target.
Our Collins (and the future submarine) are transitioning at 10+ knots, have a much bigger crew, a much more power hungry combat system. So what is practical on Type 212/214 will not be true for the Type 216 (and that is a power consumption far beyond the fuel cell AIP on board Type 212/214 can practically provide). So even the Type 216 [needs to] have 4 diesel engines (twice the number on board type 214) in order to recharge the LIB fast enough.
Soryu has a higher transitioning speed, have a much bigger crew and a more power hungry combat system than the type 214/212. Not as ["crazy" high?] as our Collins but it is more close to "reality" than the spec. of type 216 on newspapers.
Australia's Rex Patrick writing for ASPI's Strategist website reinforces the high power consumption needs of the combat system point.
[More detailed Rex Patrick views on the AN/BYG-1 are in the Asia Pacific Defence Reporter (APDR) Vol. 41 No. 8 (subscription) October 2015, pp. 36-39. APDR has commentary on Australian future submarine issues in all of its (usually monthly) editions.]
Advocates for German and French submarines frequently mention the value of AIP systems or submarines (like the Type 212 and 214) which are specifically built around AIP systems.
AIP however never appears to have been rated as a high requirement for Australian submarines. The Collins planners could have included AIP as fitted or retrofitted. Of the Collins major faults, diesel engine reliability and diesel fuel tank problems have been mentioned. Perhaps electrical reliability is also a problem. The lack of AIP has not featured on the media fault list.
AIP has also not been a major item in the future submarine debate. So
1. Maybe the US combat system's high electrical power needs effectively cancels out the AIP option.
Another assumption may be the high electrical needs of motors during the standard fast and long transit legs of (likely) most Australian sub missions. So:
2. Fast transit speeds preference large engine capacity and high (LIB) battery capacity which further pushes AIP down the requirements list.
The French response made on Submarine Matters that AIP may be retrofitted if it is thought necessary, may not be a weakness at all.